This invention relates to combustors for gas turbine engines, and in particular to wall elements for use in wall structures of combustors of gas turbine engines.
It is known to construct combustors of gas turbine engines with radially inner and outer double-walls, each having an external wall and an internal wall, the internal wall being formed of a plurality of tiles or other similar wall elements. Air is passed between the internal and external walls to provide cooling. Some of this air passes onto the hot side of the internal walls through effusion cooling holes to form a film of cooling air thereover.
The tiles typically overlap, often with a relatively cooler side of an upstream tile overlapping a hotter side of a downstream tile. This means that cooling air from the cooler side of the upstream tile can pass onto the hotter side of the downstream tile. Some air will also normally pass around the edge of a tile from the cooler side to the hotter side thereof.
Projections such as pedestals are generally provided on the rear of the tiles, extending toward the outer wall, to provide heat transfer. Cooling of the tiles therefore takes place on the cooler side by convection from the projections, and on the hotter side by film cooling. The pedestals are typically arranged in staggered rows to maximise heat transfer. In a prior art tile the array of pedestals are of uniform size and are arranged in a uniform pitch and spacing. For tiles that experience hot spots, such as those immediately downstream of a fuel injector, this arrangement is sufficient to cool the tile, however, there remains a significant thermal gradient across the tile. The thermal gradient gives rise to differential thermal expansions and contractions and consequently internal differential thermal stresses. Such differential thermal stresses, during engine flight cycles, cause thermal fatigue in the tile material and limits the service life of the tile.
The object of the present invention is therefore to maintain a more constant temperature throughout a tile and therefore reduce the thermal gradient and increase the life of the tile.